Power press slide interference prevention assembly



March 28, 1961 D. T. KENNEDY 2,976,832

POWER PRESS SLIDE INTERFERENCE PREVENTION ASSEMBLY Filed March 22. 1956 3 Sheets-Sheet 1 INVENTOR DHN/EL 7. KENNEDY BY LSJRMI TTORNEY ORNEY March 28, 1961 D. T. KENNEDY 2,976,832

POWER PRESS SLIDE INTERFERENCE PREVENTION ASSEMBLY 3 SheetsSheet 2 Filed March 22. 1956 INVENTOR EL T KENNEDY BY March 28, 1961 D. T. KENNEDY 2,975,832

POWER PRESS SLIDE INTERFERENCE PREVENTION ASSEMBLY Filed March 22, 1956 3 Sheets-Sheet 3 I258 fag) 300 I325 320 M 3/8 ra/ L; ad l 0 5Z\ ("647- W 294j-fi z 27 74 Z70 276 1 Z75 INVENTOR.

DHN/EL T KENNEDY F5 3 MLfiQmw United States Patent T1 POWER PRESS SLIDE INTERFERENCE PREVENTION ASSEMBLY Daniel T. Kennedy, La Grange Park, Ill., assignor to Danly Machine Specialties, Inc., Chicago, 111., a corporation of Illinois Filed Mar. 22, 1956, Ser. No. 573,252

7 Claims. (Cl. 113-38) My invention relates to a power press slide interference prevention assembly and more particularly to a power press slide interference prevention assembly for preventing damage to a power press owing to interference between the reciprocating slides of the press.

Power presses of the prior art are made with a number of vertical reciprocating slides carried by the press frame. One type of press includes a blank holder slide which is driven to hold the work against the press bed. An inner slide is mounted for vertical reciprocating movement within the blank holder slide. As the press operates, a die carried by the inner slide cooperates with a die carried by the press bed to form the work during a period of dwell of the blank holder. Presses of the prior art are equipped with individually operable means for adjusting the positions of the blank holder slide and inner slide on the press frame. It will be appreciated that the positions of the slides may be readily adjusted to accommodate varying thicknesses of work anddifierent size dies. In certain cases itis possible to adjust the relative positions of the blank holder and inner or working slides so that the inner slide face extends below the face of the blank holder slide. For the usual press operations, operation of the press in this manner will not injure the press since the opening in the face of the blank holder slide is large enough to permit this movement of the inner slide. 7

Where relatively small parts are being formed on the press, the dies occupy only a minor portion of the surface area of the face of the inner slide of the press. In such cases an adapter plate having an opening through which the inner slide die may pass is secured to the face of the blank holder slide. This is done in order that the work may firmly be held against the press bed adjacent the area on which the inner slide die is to perform work. If the relative positions of the blank holder and inner slides are adjusted so that the inner slide is driven to move beyond the face of the blank holder slide, it will engage the blank holder slide adapter and severe damage to the working parts of the press will result.

I have invented a power press slide interference prevention assembly which prevents damage to the press owing to adjustment of the relative positions of the press slides when the blank holder slide carries an adapter. My assembly limits the approach of the inner slide face to the face of the blank holder slide to prevent the inner slide face from extending beyond the face of the blank holder slide. I accomplish this object by providing means for disabling the slide adjustment drive means when the face of the inner slide approaches Within a predetermined distance of the face of the blank holder slide.

One object of my invention is to provide a power press slide interference prevention assembly for protecting the press against damage when the blank holder slide carries an adapter.

A further object of my invention is to provide a power press slide interference prevention assembly which limits 2,976,832 Patented Mar. 28, 1961 the approach of the press inner slide face to the face of the blank holder slide.

A still further object of my invention is to provide a power press slide interference prevention assembly which disables the press slide position adjusting means when the inner slide face approaches within a predetermined distance of the face of the blank holder slide.

Other and further objects of my invention will appear from the following description.

In general, my invention contemplates the provision of a power press slide interference prevention assembly for a power press having independently adjustable blank holder and inner slides. The adjustment for each slide includes a motor which drives a linkage to raise or lower the slide with respect to the press frame to determine the lowermost excursion of the slide. i[ provide means for producing electrical signals proportional, respectively, to the respective positions of the slides on the press frame. A comparing means compares the electrical position signals to obtain a difference signal which is proportional to the separation between the planes of the, faces of the respective slides. I provide means responsive to the difference signal for interrupting the adjusting motor circuits when the face of the inner slide approaches within a predetermined distance of the face of the blank holder slide.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure 1 is a sectional View of a power press with which my power press slide interference prevention assembly is used, with parts broken away.

Figure 2 is a top plan view of the power press with which my power press slide interference prevention as sembly is used, with the top of the press frame removed, drawn on an enlarged scale and taken along the line 22 of Figure 1.

Figure 3 is a schematic view of one form of electrical circuit which may be used with my power press slide interference prevention assembly.

More particularly referring now to Figures 11 and 2 of the drawings, the power press with which my slide interference prevention assembly is used includes a frame, indicated generally by the reference character 10, mount ed by any convenient means on a supporting floor 12. Frame 10 includes a crown 14 secured to the frame by any convenient means such as bolts or the like. I mount the blank holder slide 16 of my press, for vertical re ciprocating movement with respect to frame 10, by means such as gibs 18, 20, 22, and 24 located at the four corners of the slide 16. Pairs of gibs 18 and 2t] and 22 and 24 are supported by respective frame members 26 and 28.

A bracket 30 pivotally carried on a pin 32 mounted in a bracket 34 supported by frame 16 carries a drive motor 36 which drives belts 38 or the like to drive the press flywheel 40. Flywheel 40 is adapted to be engaged in a manner known to the art with the drive mechanism of the press. A housing 42 secured to the press frame by means such as bolts 44 contains the press drive. The blank holder slide drive means includes four links 46 which are reciprocated by the press drive mechanism, which is well known in the art, whenever flywheel 40 is clutched to the press drive shaft. I connect each of the links 46 by means of a pin 52 to a respective sliding block 48 disposed in a housing 50 formed on the blank holder slide 16.

I thread one end of a respective stud 54 into each of the sliding blocks 48. As can be seen by reference to Figure 2 of the drawings, I thread respective adjusting nuts 56, 58, 60, and 62 on the ends of the studs 54- remote from blocks 48. Supports 64 formed in housings 50 and cover plates 66 secured to the tops of the housings by any convenient means retain nuts 56, 58, 60, and 62 in 7 position within housings 50. It will be appreciated that if the adjusting nuts are rotated, studs 54 and blocks 48 will move up or down with respect :to housings 50 owing to the engagement of the respective stud threads with mating threads in the bores of nuts 56, 58, 60, and 62. I form each of the nuts 56, 8, 60, and 62 with peripheral worm teeth 68 adapted to be engaged by a worm to drive the nuts.

A platform 70 secured to the blank holder 16 by bolts 72 carries a drive motor 74. A housing 76 mounted by any convenient means on support 70 houses reduction gearing driven by motor 74 to drive a pair of :output shafts 78 and 80. A flexible coupling 82 connects shaft 78 to a shaft 84 rotatably supported in a housing 86 carried by the blank holder slide 16. A worm SS-Carried byshaft 84 for rotation with it engages the teeth '68 of nut 56 to rotate the nut when motor 74 is energized to drive shaft '78. A flexible coupling 90 connects shaft 80 to a shaft 92 rotatably supported in a housing 94 carried by the blank holder slide 16. A worm 96 mounted on shaft 92 for rotation with it drives nut 58.

Shaft 84 carries for rotation with it a bevel gear 98 which drives a bevel gear 100 fixed on a shaft 102 rotatably supported on the blank holder slide. Shaft 102 carries for rotation with it a second bevel gear 104 which drives a gear 106 fixed on a shaft 108 rotatably supported in a housing 110 on the blank holder slider Shaft 108 also carries for rotation with it a worm 112 which drives nut 62. A flexible coupling 114 connects shaft 108 to a shaft 116 connected by a flexible coupling 118 to a shaft 120 rotatably supported in a housing 122. Shaft 120 carries for rotation with it a worm 124 which drives nut 60. From the foregoing it will be seen that when motor 74 is energized to drive shafts 78 and 80, all the nuts 56, 58, 60, and 62 are driven to raise or lower the blank holder slide with respect to the press frame.

The power press with which my slide interference prevention assembly is used includes an inner slide 126 supported within the blank holder slide 16 by bearings 128 disposed adjacent the respective corners of the inner slide. When flywheel 40 is clutched to the press drive mechanism, a pair of inner slide drive links 130 are reciprocated vertically in a manner known to the art. Respective pins 132 pivotally connect links 130 to sliding blocks 134 disposed within housings 136 formed on the inner slide.' I threadedly mount blocks 134 on respective studs 138 and 140. Studs 138 and 140 carry respective adjusting nuts 142 and 144. A plate 146 carried by the inner slide 126 supports nuts 1.42 and 144. Housings 150 and 152 secured to plate 146 by any convenient means retain the nuts 142 and 144 in position on the plate 146. From the foregoing it will be appreciated that as nuts 142 and 144 are rotated, inner slide 126 is raised or lowered with respect to frame 10. I form nuts 142 and 144 with peripheral teeth 154- adapted to be engaged by worms to rotate the nuts Plate 146 mounts a motor 156 by means such as screws 158. Motor 156 drives reduction gearing contained in a housing 166 secured to plate 146 by bolts 162. When motor 156 is energized to drive the gearing in housing 160, a pair of shafts 164 and 166 rotate. Respective flexible couplings 168 and 170 connect shafts 164 and 166 to shafts 172 and 174 rotatably mounted in housings 176 and 178 carried by the inner slide. Shafts 172 and 174 carry for rotation with them respective worms 180 and 182 which drive nuts 142 and 144. When motor 156 is energized, shafts 172 and 174 drive nuts 142 and 144 to raise or lower the inner slide 126 with respect to the frame 10.

I provide means for obtaining anelectrical signal which is proportional to the position of the blank holder slide 16 with respect to the press frame. As can be seen by reference "to Figure 2, shaft carries for rotation with it agear 184 which drives a gear 186 carried by the input shaft 188 of reduction gearing housed in a housing 190 secured to support 70 by means such as bolts 192. Any convenient means secures gear 186 to shaft '188 for rotation with it. A flexible coupling 194 connects the output shaft 196 of the reduction gearing in housing 190 to the drive shaft 198 of a potentiometer 200 carried by support 70. As shaft 80 rotates, it drives shaft 198 through gears 184 and 186 and through reduction gearing in housing 190 to produce, in a manner to be described in detail hereinafter, an electrical signal which is proportional to the position of slide 16 with respect to frame 10, with the blank holder slide drive in a fixed position. In other words the signal produced is a function of the adjustment of the blank holder slide.

I provide similar means for producing an electrical signal which is proportional to the adjusted position of inner slide 126 with respect to frame 10. Shaft 164 carries for rotation with it a gear 202 which drives a gear 204 carried by the input shaft 206 of reduction gearing housed in a housing 208 secured .to the plate 146 by means such as bolts 210. The reduction gearing in housing 208 includes an output shaft 212 connected by a flexible coupling 214 to the drive shaft 216 of a potentiometer 218 carried by plate 146. As shaft 172 turns, it drives shaft 216 through gears 202 and 204 and through the reduction gearing in housing 208 to produce, in a manner to be described in detail hereinafter, an electrical signal which is proportional to the position of slide 126 with respect to frame 10, with the inner slide drive in a fixed position.

Referring now to Figure 3, shaft 198 drives the brush 220 of potentiometer 200 along the resistance winding 222 of the potentiometer. Shaft 216 drives the brush 224 of potentiometer 218 along the resistance winding 226. I connect resistance windings 222 and 226 in parallel across a source 'of direct current potential such as a battery 228. It will be appreciated that potentiometers 200 and 21-8 and battery 228 are connected in a Wheatstone bridge circuit, the resistance arms of which are determined by the respective positions of brushes 2'20 and 224 on respective resistances 2 22 and 226. If brushes 220 and 224 engage corresponding points on their respective resistance windings 222 and 226, no potential difference exists between the two brushes. If the brushes 220 and 224 are displaced relative to each other, a potential difference develops between the brushes of a magnitude proportional to the relative displacement between the brushes. Since shaft 198 is driven in accordance with the adjustment of blank holder slide 16 on frame 10, brush 220 engages a point on resistance winding 222 corresponding to the adjustment of the blank holder slide 16. Similarly, since shaft 216 is driven in accordance with the adjustment of the inner slide 126 with respectto frame 10, brush 224 engages a point on resistance winding 226 corresponding to the adjustment of the inner slide 126 on the frame. Thus the portions of the respective resistance windings 222 and 226 on the same side of brushes 220 and 224 carry respective voltages which are proportional to the adjustments of the blank holder slide and inner slide with respect to the frame 10. My Wheatstone bridge circuit compares these two voltages to obtain a difference signal which is proportional to the separation between the faces of the blank holder and inner slides at a predeterminedpoint, such as bottom dead center of the inner slide.

A conductor 230 connects brush 224 to a brush 232 which engages a voltage dividing resistor 234 connected across a bias battery 236. vA conductor 23-8 connects one common terminal of resistor 234 and battery 236 to one terminal of the control winding 240 of a magnetic amplifier 242. A current limiting or ballast resistor 244 connects brush 220 to winding 240. The respective polarities of batteries 228 and 236 are such that the voltaevasaa age divider potential between brush 232 and conductor 238 acts in opposition to the difference voltage between brushes 220 and 224. In other words, the difference signal between brushes 220 and 224 is the control signal input for magnetic amplifier 242 while battery 236 and voltage dividing resistor 234 provide a bias acting against this control signal. Amplifier 242 includes a pair of output windings 246 and 248, one terminal of each of which is connected to a common conductor 250 which is connected to one terminal 252 of a source of threephase electrical potential (not shown) which potential appears at terminals 252, 254, and 256. I connect the other respective terminals of output windings 246 and 248 to two of the terminals of a full wave bridge rectifying circuit including a plurality of rectifiers 258. A common conductor 260 connects another two terminals of the rectifier bridge to terminal 254. 1 connect a relay winding 262 between the output terminals 264 and 266 of the bridge rectifier which includes unidirectional current devices such as crystals or the like 258.

When the control signal input to winding 24% increases, the output signal between terminals 264 and 266 increases. Respective conductors 268 and 270 connect terminals 252 and 256 to pairs of respective contacts 274 and 272 and 278 and 276 of reversing switches, indicated generally, respectively, by the reference characters 280 and 282. Switch 289 includes a pair of ganged contact arms 284 and 286 connected by respective conductors 288 and 290 to a pair of input terminals 282 and 294 of the inner slide drive motor 156.

Switch 282 includes a pair of ganged contact arms 296 and 298 connected by respective conductors 300 and 302 to a pair of input terminals 364 and 306 of the blank holder adjusting motors to conductor 260 which is connected to terminal 254.

With arms 284 and 286 in engagement with contacts.

272 and 274, and with arms 296 and 298 in engagement with contacts 276 and 278, motors 156 and 74 are energized to drive the inner slide up and to drive the blank holder slide down with respect to the press frame. It will be appreciated that when the inner slide and blank holder slide are moving in these directions, their relative motion is away from each other and no problem of possible slide interference exists. As a result, it will not become necessary to interrupt the drive motor circuits for these directions of movement. With the pair of arms 284 and 286 engaging contacts 272 and 274 and with the pairs of arms 296 and 298 engaging the contacts 276 and 278 to drive motors 156 and 74 in these directions, brushes 224 and 220 both are driven in a counterclockwise direction to move them relatively away from each other to increase the voltage difierence appearing between brushes 224 and 220.

I provide circuits for reversing drive motors 156 and 74 adjustably to lower the inner slide and raise the blank holder slide. Switch 280 includes a pair of reversing contacts 314 and 316 connected by respective conductors 318 and 320 to conductors 324 and 322. A pair of normally open switches 325 and 326 connect respective conductors 322 and 324 to conductors 27d and 268. Conductors 322 and 34 also connect respective reversing contacts 330 and 328 of switch 282 to switches 325 and 326. When the inner slide is to be lowered, arms 284 and 286 are engaged with contacts 314 and 316 to reverse drive motor 156 to move brush 22-4 in a clockwise direction as viewed in Figure 3. Similarly, when the blank holder slide is to be raised, arms 2% and 298 are engaged with contacts 328 and 330 to reverse drive motor 74 to drive brush 220 in a clockwise direction as viewed in Figure 3. When a blank holder adapter is being used and either the inner slide is moving down or the blank holder slide is moving up, or at any time when the relative motion of the slides is toward each other, a problem exists of limiting the approach of the slides to one another in order that damage to the press be avoided.

It also will be appreciated that when either of the brushes 220 or .224 is moving in a clockwise direction or when both brushes are moving in a clockwise direction from the positions shown in Figure 3, the potential difference between the brushes decreases until the brushes occupy corresponding positions. Since this potential difference is decreasing, the output voltage between terminals 264 and 266 decreases. I select the bias provided by the positioning of brush 232 to cause the output voltage from amplifier 242 to drop to a level below that which will energize winding 262 when the faces of the inner and blank holder slides approach each other within a pre determined distance. When winding 262 is de-energized, switches 325 and 326open, with the result that the circuits of motors 156 and 74 cannot be energized to raise the blank holder slide or to lower the inner slide. The circuits of motors 156 and 74v can, however, be completed to lower the blank holder and to raise the inner slide. When suflicient potential difference between brushes 220 and 224 exists, an output signal. will be produced. This signal energizes winding 262 thus closing switches 325 and 326 through a linkage 327. If the switches are closed, the circuits of motors 156 and 74 may be completed to lower the inner slide and to raise the blank holder. The limit of approach of the slides may readily be adjusted by moving brush 232 along resistor 234 to vary the position at which relay winding 262 is energized and de-energized.

In operation of my power press slide interference pre vention assembly, in order to lower the blank holder slide, arms 296 and 298 are engaged with contacts 276 and 278 to complete the circuit of motor '74 to lower the blank holder slide. In this condition of switch 282, brush 220 is driven in a counterclockwise direction. In order to raise the inner slide, arms 284 and 286 are engaged with contacts 272 and 274 to complete the circuit of motor 156 to raise the inner slide. In this condition of switch 280, brush 224 is driven in a counterclockwise direction. The positions of brushes 220 and 224 shown in Figure 3 correspond approximately to the lowest position of the blank holder slide and the highest position of the inner slide with respect to the press frame. Stated differently, the brush 224 is adapted to produce a potential which is the analogue of the adjusted position of the inner slide with respect to the frame. The brush 220 is adapted to produce a signal which is the analogue of the adjusted position of the blank holder with respect to the frame. It will also be observed that the position of the brush 232 represents the signal which is the analogue of the closest approach the inner slide is to make to the blank holder during the period of slide adjustment. The press is inched until the blank holder reaches the bottom of its stroke and begins to dwell. In the position shown in the drawing the blank holder has been moved adjacent its lowermost position of slide adjustment and the inner slide has been moved to a position adjacent its uppermost position of slide adjustment. It will be appreciated that in this relative position of the brushes a large potential difference exists between the brushes. This potential difference causes current to flow in winding 240 partially saturating the core of the winding 262. This increased output signal from ampliher 242 is sufficient to energize winding 262 to close switches 325 and 326. After the brush 232 has been set to determine a safe distance, the press may be inched and the inner slide moved downwardly to the bottom of its stroke. Any adjustments may be made by means of the slide adjustment motors. It will be impossible to move the slides by means of the adjustment motors to produce an interference owing to the construction of my invention.

When the position of the inner slide is to be adjusted by lowering it with respect to the blank holder slide,

switch arms 284 and 236 are engaged with contacts 314 and 316 to complete the circuit of motor 156 to lower the inner slide. In this condition of switch 280, brush 2-24 is "driven in a clockwise direction to reduce -the potenfial difference between brushes 224 and 220 to reduce the output signal "from amplifier 242. At a point determined by the biasing voltage divider 234, the output signal from amplifier 242 will not be suiiicient to energize winding 262, and switches 325 and 326 open to interrupt the circuits of drive motors 156 and 74. Brush 232 isset on resistor 234 to interrupt the drive motor cir cuits when the faces of the inner and blank holder slides approach within a predetermined distance of each other.

When the blank holder slide is to be moved up with respect to the inner slide, switch arms 2,96 and 298 are engaged with contacts 328 and 33K}- to energize motor 7'4 to raise the blank holder slide. In. this condition of switch 282 brush 22!) moves in a clockwise direction to decrease the potential difference between brushes 22$ and 224 to decrease the output signal from amplifier 242. At a predetermined point determined by the bias on the amplifier, the output signal from amplifier 242 will not be sufiicient to energize winding 252, with the result that switches 325 and 326 open. When this occurs, the slide adjusting drive motors are de-energized. It is to be understood that my assembly works as well when both the blank holder and inner slide adjusting means are being driven simultaneously as when only one of the adjusting means is being driven.

It will be seen that I have accomplished the objects of my invention. -1 have provided an assembly for preventing interference between the slides of a power press or the like. My assembly is particularly advantageous where blank holder adapters are being used on the press. My system interrupts the circuits of the adjusting means drive motors when the faces of the inner and blank holder slides approach to within a predetermined distance of each other.

If desired the output of the bridge appearing across adjustable arms 224 and 220 may be used directly to control the relay winding 262 eliminating the magnetic amplifier. In this case, of course, the voltage of the potential source 228 will have to be large enough to energize the relay winding 262.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention What I claim is:

1. In a power press having a frame, a first slide mounted for reciprocating movement on said frame, a second slide mounted for reciprocating movement on said frame and respective drives for reciprocating said slides, a slide interference prevention assembly including means comprising a motor and a circuit for energizing said motor for adjusting the position of said first slide with respect to the frame, means comprising a second motor and a second circuit for energizing said second motor for adjusting the position of said second slide with respect to the frame, means for producing a first electrical signal proportional to the position of adjustment of said first slide on said frame, means for producing a second electrical signal proportional to the position of adjustment of said second slide on the frame, means for comparing said signals to produce a diiferenc'e signal, means for producing a predetermined electrical signal corresponding to a desired minimum separation of said slides, means for comparing said predetermined signal and said difference signal to produce a control signal and means responsive to said control signal for interrupting said motor circuits for disabling said adjusting means when said slides approach each other under the action of said position adjusting means within a distance corresponding to a predetermined minimum separation of said slides in operation'of'the'press.

2. In a power press having a frame, 'a blank holder slide, an inner slide, respective means mounting said slides for reciprocating movement on said frame and respective main drive means for said inner slide and for said blank holder slide, a slide interference prevention assembly including a first auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said blank holder slide with respect to said frame, an electrical circuit for energizing said blank holder adjusting motor, second auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said inner slide with respect to said frame, a circuit for energizing said inner slide adjusting motor, means for producing a first electrical signal proportional to the position of adjustment of said blank holder slide on said frame, means for producing a second electrical signal proportional to the position of adjustment of said inner slide on said frame, means for comparing said electrical signals to produce a difference signal proportional to the distance separating the adjusted positions of said inner slide and said blank holder slide, means for producing a predetermined electrical signal corresponding to the desired minimum separation of said slides, means for comparing said predetermined signal and said difference signal to produce a control signal and means responsive to said control signal for interrupting said auxiliary drive means motor circuits when said slides approach each other under the action of said auxiliary drive means within a distance corresponding to a predetermined minimum separation of said slides under the action of said main drive means in operation of the press.

3. In a power press having a frame, a blank holder slide, an inner slide, respective means mounting said slides for reciprocating movement on said frame and re spective main drive means for said inner slide and for said blank holder slide, a slide interference prevention assembly including a first auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said blank holder slide with respect to said frame, an electrical circuit for energizing said blank holder adjusting motor, second auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said inner slide with respect to said frame, a circuit for energizing said inner slide adjusting motor, means comprising a potentiometer having a brush driven by said blank slide adjusting shaft for producing a first electrical signal proportional to the position of ajustment of said blank holder slide on said frame, means comprising a potentiometer having a brush driven by the inner slide adjusting shaft for producing a second electrical signal proportional to the position of adjustment of said inner slide on said frame, means for comparing said electrical signals to produce a difference signal proportional to the distance separating the adjusted positions of said inner slide and said blank holder slide, means for producing a predetermined electrical signal corresponding to the desired minimum separation of said slides, means for comparing said predetermined signal and said difference signal to produce a control signal and means responsive to said control signal for interrupting said auxiliary drive means motor circuits when slides approach each other under the action of said auxiliary drive means within a distance corresponding to a predetermined minimum separation of said slides under the action of said main drive means in operation of the press.

4. In a power press having a frame, a blank holder slide, an inner slide, respective means mounting said slides for reciprocating movement on said frame and respective main drive means for said inner slide and for said blank holder slide, a slide interference prevention assembly including a first auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said blank holder slide with respect to said frame, an electrical circuit for energizing said blank holder adjusting motor, second auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said inner slide with respect to said frame, a circuit for energizing said inner slide adjusting motor, means for producing a first electrical signal proportional to the position of adjustment of said blank holder slide on said frame, means for producing a second electrical signal proportional to the position of adjustment of said inner slide on said frame, means for comparing said electrical signals to produce a difference signal proportional to the distance separating the adjusted positions of said inner slide and said blank holder slide, means for producing a predetermined electrical signal corresponding to the desired minimum separation of said slides, means for comparing said predetermined signal and said difference signal to produce a control signal, a relay having a winding and respective normally open switches in said auxiliary drive means motor circuits, a magnetic amplifier having a control winding, means for applying said control signal to said control winding and means forimpressing the output signal of said magnetic amplifier across said relay winding whereby to close said switches so long as said control signal has a magnitude which is greater than the magnitude of the signal when said slides approach each other under the action of said auxiliary drive means within a distance corresponding to a predetermined minimum separation of said slides under the action of said main drives in operation of the press.

5. A power press including in combination a frame, a first slide, a first main drive means for reciprocating said first slide on said frame, a first auxiliary drive means for adjusting the position of said first slide with respect to said first main drive means, a second slide, a second main drive for reciprocating said second slide on said frame, a second auxiliary drive means for adjusting the position of said second slide with respect to said second main drive means, means for producing a first signal which is an analogue of the position of adjustment of the first slide, means for producing a second signal which is an analogue of the position of adjustment of said second slide, means for producing a predetermined signal which is the analogue of a predetermined minimum separation between said slides under the action of said main drive means in operation of the press, means for comparing said first and second slide position analogue signals to obtain a diiference signal, means for comparing said diiference signal with said slide minimum separation analogue signal to obtain a control signal, and means responsive to said control signal for disabling said auxiliary slide drive means whereby to prevent the separa tion of said slides under the action of said main drive means in operation of the press from being less than that determined by said slide minimum separation analogue signal.

6. In a power press having a frame, a blank holder slide, an inner slide, respective means mounting said inner slide and said blank holder slide for reciprocating movement on said frame and main drive means for said slides, a slide interference prevention assembly including first auxiliary drive means comprising a motor and a drive shaft for adjusting the position of said blank holder slide with respect to the frame, an electrical circuit for energizing said blank holder adjusting motor, second auxiliary rive means comprising a motor and a drive shaft for adjusting the position of said inner slide with respect to said frame, a circuit for energizing said inner slide adjusting motor, means for producing a first electrical signal proportional to the position of adjustment of said blank holder slide on said frame, means for producing a second electrical signal proportional to the position of adjustment of said inner slide on said frame, means for comparing said electrical signals to produce a difference signal proportional to the distance separating the adjusted positions of said inner slide and said blank holder slide, means for producing a predetermined signal corresponding to the desired minimum separation of said slides, means for comparing said difference signal and said predetermined signal to produce a control signal, a relay comprising a winding and respective normally open switches in said drive motor circuits and means for impressing said control signal across said relay winding to close said switches so long as said control signal has a magnitude which is greater than that corresponding to a predetermined minimum separation of said slides under the action of said main drive means in operation of the press.

7. In a power press having a frame, a blank holder slide, an inner slide, respective means mounting said inner slide and said blank holder slide for reciprocating movement on said frame and main drive means for said slides, an assembly including in combination first auxiliary drive means for adjusting the position of said blank holder slide with respect to the press frame, second auxiliary drive means for adjusting the position of said inner slide with respect to the press frame, means responsive to the operation if said first auxiliary drive means for producing a first electrical signal representing the adjusted position of said blank holder slide on the press frame, means responsive to the operation of said second auxiliary drive means for producing a second electrical signal representing the adjusted position of said inner slide on the press frame and means for comparing said first and second electrical signals to produce a difference signal representing the separation of the adjusted positions, of said slides on said frame.

References Cited in the file of this patent UNITED STATES PATENTS 2,185,096 Treer Dec. 26, 1939 2,259,882 Glasner Oct. 21, 1941 2,550,061 Glasner et al. Apr. 24, 1951 2,750,553 Andersson June 12, 1956 UNITED STATES PATENT OFFICE CERTIFICATION- OF CORRECTION Patent-N0. 2,976,832 March 281 1961 Daniel T. Kennedy It is hereby certified'that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10 line 4L3 for "if" read of -=-q Signed and sealed this. 15th day of August 1961 (SEAL) Attest:

ERNEST W. SWIDER Y DAVID L. LADD Attesting Officer Commissioner of Patents 

